The implementation of POCUS and POCUS training for residents: the Rijnstate approach.

Point-of-care ultrasound (POCUS) is gaining interest in intensive care medicine and good reviews and guidelines on POCUS are available. Unfortunately, how to implement POCUS and practical examples how to train staff and junior doctors is not well described in literature. We discuss the process of POCUS implementation, and a POCUS training program for residents prior to their intensive care rotation in a Dutch teaching hospital intensive care unit. The described four-day basic POCUS course consists of short tutorials and ample time for hands-on practice. Theoretical tests are taken shortly before, on the last day of the course, and after three months to assess learning retention. Practical tests are taken on the last day of the course and after three months. We stress the importance of POCUS for intensive care and hope that our experiences will help colleagues who also want to go forward with POCUS.

Hemodynamic and pulmonary fluid status in the trauma patient: are we slipping?

Recent reports point to problems in the clinical assessment of the cardiopulmonary system in hemodynamically unstable patients, especially with the decreasing usage of pulmonary artery catheters. Our purpose was to evaluate the hypothesis that clinical judgment alone is inadequate for a reliable estimate of cardiopulmonary status in critically ill patients. Physician assessments (high, normal, or low) of cardiac index (CI) and thoracic fluid content (TFC) were made in 68 acute trauma cases and compared to the results obtained with impedance cardiography (ICG). Physician assessment using clinical judgment alone was correct only 42 per cent and 57 per cent, respectively, for CI and TFC. There was very little difference in heart rate (HR), blood pressure (BP), Glasgow Coma Score (GCS), and the number of injured systems between the incorrect and correct assessments of CI. However, the mean Injury Severity Score (ISS) was markedly higher for the incorrect than the correct CI values (18.8 +/- 9.3 vs 14.2 +/- 9.8, P = 0.0589). Thus, there is a need for an objective measurement of CI and TFC especially in the more severely injured patient. The inaccuracy of the clinical exam strongly suggests the need for a supplemental measurement, which the new and improved ICG monitor could provide.

Clonogenic analysis reveals reserve stem cells in postnatal mammals. II. Pluripotent epiblastic-like stem cells.

Undifferentiated cells have been identified in the prenatal blastocyst, inner cell mass, and gonadal ridges of rodents and primates, including humans. After isolation these cells express molecular and immunological markers for embryonic cells, capabilities for extended self-renewal, and telomerase activity. When allowed to differentiate, embryonic stem cells express phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin. When implanted in vivo, undifferentiated noninduced embryonic stem cells formed teratomas. In this report we describe a cell clone isolated from postnatal rat skeletal muscle and derived by repetitive single-cell clonogenic analysis. In the undifferentiated state it consists of very small cells having a high ratio of nucleus to cytoplasm. The clone expresses molecular and immunological markers for embryonic stem cells. It exhibits telomerase activity, which is consistent with its extended capability for self-renewal. When induced to differentiate, it expressed phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin. The clone was designated as a postnatal pluripotent epiblastic-like stem cell (PPELSC). The undifferentiated clone was transfected with a genomic marker and assayed for alterations in stem cell characteristics. No alterations were noted. The labeled clone, when implanted into heart after injury, incorporated into myocardial tissues undergoing repair. The labeled clone was subjected to directed lineage induction in vitro, resulting in the formation of islet-like structures (ILSs) that secreted insulin in response to a glucose challenge. This study suggests that embryonic-like stem cells are retained within postnatal mammals and have the potential for use in gene therapy and tissue engineering.

Time-frequency distribution technique in biological signal processing.

Time-frequency distribution (TFD) has gained wide acceptance for deterministic non-stationary signal processing, particularly for biological signals, in both basic research and commercial production. This paper presents the results of a comparison of the TFD technique with other methods for determining physiologic parameters, particularly the ventricular ejection time (VET) and (dZ/dtmax), the differentiation of the thoracic-fluid signal Z0 from non-stationary impedence cardiography dZ/dt. The TFD technique was found to be more accurate--in terms of both time and signal magnitude--than traditional methods such as the baseline and ensemble-averaging techniques when compared with phonocardiograms and hand calculations by experts in the field. It is shown that TFD can also reduce ventilatory/respiratory noise, electrical and muscle noise, and patient-motion artifacts. Correlation analysis and regression analysis as well as Bland-Altman studies showed stronger correlational methods tested.

An advanced signal processing technique for impedance cardiography.

A new design using the latest technique in signal processing, the time-frequency analysis method, was developed to process impedance cardiography signals. This technique, when used to determine the relevant calculation parameters, was found to be more accurate than conventional methods. It was shown to be advantageous in reducing ventilation artifacts and motion noise, resulting in greater accuracy. Its cardiac output values had a much better correlation coefficient when compared in the clinical setting to the standard thermodilution technique than did the values from conventional impedance cardiography devices.

Multicenter trial of a new thoracic electrical bioimpedance device for cardiac output estimation.

OBJECTIVE: To evaluate the capacity of a new thoracic electric bioimpedance system to estimate cardiac output compared with the conventional thermodilution method. DESIGN: Prospective, multicenter study. SETTING: A university-run county hospital, a university-run U.S. Veterans Affairs hospital, and a university-affiliated U.S. military hospital. PATIENTS: A series of 68 critically ill patients whose conditions required pulmonary artery catheter insertion. MEASUREMENTS AND MAIN RESULTS: A total of 842 simultaneous pairs of cardiac output estimations by conventional thermodilution and a new thoracic electric bioimpedance system that uses an improved signal processing technique based on an all-integer-coefficient filtering technology, using a time-frequency distribution that provides a high signal/noise ratio were evaluated. The r value was .86, r2 = .74, and p < .001 by regression analysis; the mean difference between the two methods relative to their average value was 16.6 +/- 12.9 (SD) %; the precision was 1.4 L/min or 0.8 L/min/m2; the bias was -0.013 L/min. The mean difference between successive pairs of thermodilution measurements was 8.6 +/- 0.6 (SD) %, which was about half the difference between simultaneous pairs of measurement by the two methods. The changes in impedance estimations were close to simultaneously measured changes in thermodilution estimates of cardiac output. CONCLUSIONS: The new bioimpedance system satisfactorily estimated cardiac output as measured by the thermodilution technique. The difference between the two estimations is more than made up for by the continuous noninvasive capability of the impedance system.

An impedance cardiography system: a new design.

An IBM compatible impedance cardiac output monitoring prototype system has been developed for use at the bedside on patients in the ICU, CCU, ER, Cath. Lab, and OR, etc. This impedance cardiographic (ICG) system, whose operation is completely technician-free, provides a continuous display with digital results and four channel color waveforms on an Enhanced Graphics Display screen. The software is written in C language with several special segments in assembly code where speed is essential. In this prototype system, a real-time algorithm was introduced to modify the ensemble averaging technique so that it averages nonperiodic signals such as: ECG, dZ/dT, delta Z, etc. Also, a real-time algorithm was developed to adaptively detect R spikes from conventional ECG signals. A signal preprocessor was developed to process signals digitally before any further work is done. This procedure reduces muscle noise, 60 Hz interference, and ventilatory movement. A special digital filter was designed to cope with the cases in which pacemakers are used. A special algorithm was also developed to further reduce the ventilation artifacts so that a period of apnea is unnecessary during the performance of the measurements. An anatomically specified electrode configuration has been defined enabling precise and reproducible positioning of the electrodes--hopefully leading to electrode standardization. At the present time, this prototype system has been compared with standard hand calculation and correlated with the clinical "gold standard," the Swan-Ganz thermodilution cardiac output. Using 144 sets of data from 10 healthy volunteers, 4 critically ill patients, and 8 healthy exercising volunteers, calculations of cardiac output were made using our system and the standard hand calculation of stroke volume, based upon Kubicek's equation; there was a relatively high and stable correlation: r = 0.93, p less than 0.005 (healthy); r = 0.94, p less than 0.002 (ill), r = 0.95, p less than 0.002 (exercise). From 20 patients at two different hospitals all with Swan-Ganz catheters in their hearts, 65 correlation studies between our system and the standard thermodilution technique were performed; the results were encouraging in terms of accuracy and consistency (r1 = 0.84, p less than 0.01, n = 10 CCU patients), and (r2 = 0.93, p less than 0.01, n = ICU patients). These results along with a growing body of data from other investigators indicate that this noninvasive and technician-free system for measuring cardiac output could have a significant role in patient care.

Impedance cardiography. Current status and clinical applications.

Impedance cardiography is a highly reproducible, rapid and safe method for the evaluation of cardiac performance in the clinical setting. Measurements of stroke volume (SV), end diastolic volume (EDV), and end systolic volume (ESV) with calculation of cardiac output (CO) were obtained in normal, healthy people (group 1, n = 21) and in patients with congestive heart failure (group 2, n = 18). Individuals were placed on a tilt table and cardiac profiles (measurements of CO, SV, EDV, and ESV) were performed at 45 degrees head up, 15 degrees head up, and supine. Group 1 responded by increasing CI from 2.9 +/- 0.81 L/min/M2 at 45 degrees to 3.3 +/- 1.0 L/min/M2 at 15 degrees to 3.7 +/- 1.0 L/min/M2 supine. There was no corresponding rise seen in group 2, with CIs of 2.1 +/- 0.83 L/min/M2, 2.0 +/- 0.78 L/min/M2 and 2.0 +/- 0.76 L/min/M2 at each position, respectively. In addition, while the EDV increased at each position in group 1 (45 degrees: 71 +/- 21 cc/M2, 15 degrees: 88 +/- 26 cc/M2, Supine: 102 +/- 29 cc/M2), no such increase was evident in group 2 (45 degrees: 57 +/- 29 cc/M2, 15 degrees: 52 +/- 20 cc/M2, Supine: 60 +/- 24 cc/M2). The inability of group 2 patients to elevate CI and the absence of any discernible change in EDV suggests an insufficiency of cardiac reserve with noncompliant ventricles. This information is currently being used to assess operative risk and to study effects of treatment modalities.

Vascular distensibility and vascular surgery.

The elastic property of an arterial wall decreases considerably with aging and/or with a variety of pathological conditions. The resulting decrease in vascular compliance has a profound physiological effect on arterial perfusion. The objectives of this study were to assess a quantitative measure of peripheral vascular distensibility (D), to apply it in some clinical conditions, and to establish a potential means of predicting success in vascular surgery for limb salvage. A technique described earlier by us for the determination of D based on an accurate measurement of volume change (delta V) with pressure change (delta P) was further analyzed and then tested in four groups: the first two were non-surgical, 18 normal subjects, and 23 hypertensive men paired with 22 normotensive men; the last two were surgical, patients undergoing aortofemoral bypass (AFB) operations for limb salvage (salvaged vs unsalvaged); and patients who underwent below-knee amputations (BKA) for severe arterial insufficiency (healed vs unhealed). The results indicate that D can be used as a reliable assessment of the pathophysiological status of the arterial system in the lower extremity; furthermore, D can be used as a predictor of success in at least two types of vascular procedures: AFB with profundoplasty for limb salvage and BKA for severe arterial insufficiency.

Screening for the potential pulmonary embolism victim.

The venous hemodynamics of 134 legs were evaluated using a bilateral impedance plethysmograph. Calf venous outflow following the release of proximal occluding cuffs and calf volume changes with ventilation were compared with the results of venography. We found that a two-second outflow of at least 65% indicated a patent deep venous system while an outflow of 50% or less indicated an obstruction of the proximal deep venous system. With outflow between 50% and 65%, a ventilatory wave height greater than 3 mm ruled out proximal deep venous obstruction while a height of 3 mm or less was not diagnostic. These two criteria yielded an accuracy of 92% with no false-negative results and a false-positive rate of only 10%. Thus, this technique can accurately rule out proximal deep venous obstruction and give the clinician considerable confidence in initiating anticoagulant therapy on those suspected cases with positive studies.

Predicting success in limb salvage.

While success in revascularization procedures for severe arterial insufficiency--limb salvage--demands a technically correct operation, the adequacy of the outflow system is equally important. An outflow index (phi), the percentage drop in femoral artery pressure following an intra-arterial injection of papaverine, was developed. The predictive value of this index was demonstrated in a prospective study of 44 limbs in which an aortoiliac procedure with profundoplasty was done for multilevel disease. In the operations considered completely successful (n = 27), the mean value of phi was 37 +/- 8 per cent; this was significantly greater (P less than 0.001) than the mean value of 16 +/- 9 per cent found for those operations (n = 17) deemed to have been unsuccessful on the basis of rigorous postoperative criteria. This finding not only proves the efficacy of the index, but emphasizes the importance of an outflow system with the ability to accept more blood.

Calibrated impedance plethysmograph.

The accuracy of quantitative pulse-volume measurement with a calibrated electrical impedance plethysmograph was determined on a laboratory limb-segment model. Changes in electrical impedance detected via a tetraprolar electode configuration were related to pulse-volume changes by the parallel-impedance model described by Nyboer et al. (The Impedance Plethysmograph: An Electrical Volume Recorder. Natl. Res. Council, Comm. Aviation Med. 149, 1943). The instrument employed in this study calculated pulse volume assuming two standard conditions: distance between voltage electrodes, l, is 15 cm, and resistivitiy of blood, rho b, is 150 omega x cm. The effects of varying tissue and blood resistivity, pulse frequency, and electrode distance were investigated. Measurements under three ionically distinct conditions gave an overall accuracy of 96.6% with correlation coefficients of 0.99 for each condition. Measurement accuracy was maintained with a pulse-frequency variation in the range of 15-150 pulses/min and with application of correction factors for electrode distance and blood resistivity other than the standard values.

The calibrated impendance plethysmograph: laboratory and clinical studies.

By careful experimental studies a calibrated impedance plethysmograph has been shown to be highly accurate (standard error = 3.8%). Its ability to measure the rate of pulsatile volume change has been extremely useful in the diagnosis of arterial insufficiency of the lower extremities. By helping in the objective definition and documentation of arterial perfusion, this instrument can greatly improve our selectivity of patients for angiography and subsequent revascularization.

Noninvasive assessment of vascular disease in the lower limbs of diabetics.

One hundred and fifty seven limbs of diabetic patients free of any symptoms or signs of arterial insufficiency, were studied using noninvasive techniques to determine vascular distensibility in the lower extremities. A relationship between these values and the classification of the diabetic in terms of age, duration of diabetes and control of diabetes was sought. The results revealed a distinct inverse relationship between vascular distensibility and age of the diabetic subject, analogous to the trend found in a normal, non-diabetic group of volunteers. Furthermore, comparison of distensibility in normal and diabetic subjects within the same age group showed lowered values among the diabetics. However, the study revealed little or no apparent relationship to either duration or control of diabetes.

Hyperemic response for accurate diagnosis of arterial insufficiency.

Monitoring of calf (or ankle) blood pressure during reactive hyperemia after thigh arterial occlusion allows differentiation of normal from abnormal responses and of distal (femoropopliteal [FP] system) disease from proximal (aortoiliac [AI] disease. The hyperemic response of 106 lower extremities representing three disease states--FP (N = 19), AI (N = 15), and combined (AI plus FP)(N = 16)--were compared with each other and with 20 normal subjects and 36 asymptomatic diabetics. Not only were the three disease states readily distinguished from the very similar normal subjects and asymptomatic diabetics, but there was a highly significant difference between FP disease and AI disease up to 150 s. This is a simple, inexpensive, and reliable test that can be used at the bedside to determine levels of severe disease, especially in the claudicator, who may not have a critical stenosis under resting conditions.

Which deep breathing device should the postoperative patient use?

A study was undertaken to compare the use of three types of deep-breathing devices in patients undergoing upper-abdominal operations. Seventy-nine patients were divided into three groups, each receiving preoperative bedside testing of pulmonary function and instruction in the use of one of three randomly assigned deep-breathing devices thought to be representative of those currently available (Triflo II, Bartlett-Edwards Incentive Spirometer, or Spirocare). Repeat testing and instruction were provided daily during each of the first five postoperative days. There were few statistically significant differences in pulmonary function, vital signs and white blood cell count, and no difference in length of postoperative stay. No device was uniformly acceptable to patients, and none was used as frequently as recommended. When left at the bedside and only one daily reinforcement of instructions, the three devices showed no clinically important differences.